GBT Spectral-Line Data Reduction and Tutorials. David Frayer (Green Bank Observatory)

Transcription

1 GBT Spectral-Line Data Reduction and Tutorials David Frayer (Green Bank Observatory)

2 Click to login into Green Bank

3 GBO startkde on Processing Machine ssh planck startkde Public Processing Machines: planck newton fourier arcturus

4 The GBT has a lot of different observation types and many different methods for reduction Standard gbtidl routines and the GBT pipeline supports VEGAS spectral-line data from positionswitched or frequency-switched observations for receivers with noise diodes Pulsar data è Presto reduction package Mustang è separate Mustang package (Mason) VLBI è VLBA folks Radar è Radar folks W-band, Argus, SubBeamNod è Frayer Data reduction not supported for continuum observations or stokes polarization observations; however, non-official software exists

5 Reduction Software Documentation GBTIDL: -- User's Guide: - Quick Reference: - Calibration documentation: - Reference Manuals: User: Contrib: sdfits: gbtpipeline: gbtgridder: (gbtgridder h)

6 GBT Data Processing Flow Chart Raw GBTdata Raw VEGAS data (1) (1) The sdfits program is used to convert raw GBT and VEGAS data into a sdfits file. (2) The sdfits data are calibrated to Ta*/Tmb/Snu within gbtidl (or the pipeline) and saved to output calibrated data file(s). (3) A co-added image per frequency bin is made using the gbtgridder program which outputs a data cube with associated weights. sdfits data Calibrated Spectra (2) (3) Image data cubes

7 The telescope measures: Ta = antenna temperature Ta(total) = Tsource + {Trx + Tbg + Tatm + Tspill} Where {.} = other contributions Want Tsource, so carry out ON OFF Ta(ON) =Tsource + {.} Ta(OFF) = {.} So Ta(ON)-Ta(OFF) = Tsource è Need to carry out ON-OFF observations and there are different observing techniques for measuring ON-OFF

8 Different Observing Modes to derive the reference data (OFF) Types of reference observations ØFrequency Switching In or Out-of-band ØPosition Switching Reference-Off Mapping-Off ØDual-Beam Position Switching Nod -- Move telescope SubBeamNod -- Move Subreflector

9 GBT Definition of Ta T a = (ON OFF) T OFF system Blank Sky or other From diodes, Hot/Cold loads, etc.

10 Determining T sys Noise Diodes All GBT receivers besides 4mm, Argus, and Mustang use noise diodes.

11 Determining T sys Noise Diodes T sys = T cal * OFF/(ON OFF) GBT: Flicker diode on/off T sys = T cal * OFF/(ON OFF) + T cal /2 Typically choose low Tcal value to minimize Tsys and high Tcal value for very bright sources (for Rx that have two options)

12 Determining T sys Hot & Cold Loads Cooling System T cold Hot Load T hot Gain: g =(Thot Tcold)/(Vhot Vcold) [K/Volts] Tsys = g Voff Example GBT 4mm Rx

13 Temperature Scales ØTa= Tsys (ON-OFF)/OFF (GBT typically uses uncorrected antenna temperature) ØTa = Ta exp(τ o A) (corrected for atmosphere) ØT mb = Ta /η mb (η mb ~1.3 η a ) ØTa* = Ta /η l ØTa /Sν =2.84 η a (for the GBT) (Argus uses Ta*, η l =~0.99 for the GBT)

14 Calibration: Flux Density vs Antenna Temp vs Main-Beam Temp P rec = ½ A e S ν Δν = k T a Δν A e =η a (π/4) D 2 S ν = 3520 T a /(η a [D/m] 2 ) èt a /S ν = 2.84 η a for the GBT (η a =0.71 at low ν) Ø Know S ν (use ALMA calibration database for 3mm and VLA calibration papers for <50GHz) and derive η a from measured Ta Ø Measure FWHM from good pointing scans or within your image to derived η mb and Tmb; Tmb = Ta / η mb Ø η mb = η a (θ FWHM 100m/ λ) 2 (assumes Gaussian beam, where beam FWHM is in radians)

15 GBO Data Directories Home area: /users/user_name Scratch data area: /home/scratch/user_name Raw gbtdata by project (e.g., AGBT16B_037_04): /home/gbtdata/agbt16b_037_04 Raw Vegas data by project: /lustre/gbtdata/agbt16b_037_04/vegas sdfits data by project: /home/sdfits/agbt16b_037/04

16 Public Data Processing Machines with lustre access: newton, planck, fourier (192GB ram) euclid, thales (16GB ram) arcturus (132GB ram) {pipeline machine} Extra disk space for data processing: /lustre/pipeline/scratch/user_name

17 gbtidl (=unipops [12m and 140ft reduction package] converted to IDL) ØData access (connecting to sdfits file) o gbtidl> online o gbtidl> offline, AGBT16B_037_04 o gbtidl> filein, mysdfitsfile.fits o gbtidl> summary ØUser pro directory used by gbtidl: /users/user_name/gbtidlpro

18 Standard Reduction scripts q Ta=Tsys(ON-OFF/OFF): getps, scan (position switch) getfs, scan (frequency switch) getnod, scan (nod data) getsigref, scan_on,scan_off q Raw passband gettp, scan (total power for scan) gettp,scan,ifnum=ifnum,plnum=plnum,fdnum=fdnum, sig_state=sig_state,subref=subref,wcalpos=wcalpos getrec, rec (get an individual record, see list)

19 Some Basic GBTIDL Commands: DEMO_basics gbtidl> offline, TGBT17A_506_11 gbtidl> summary (give summary of session) gbtidl> getsigref,6,7 (on,off position switch data reduction) gbtidl> header (provide some of the meta data in container 0) gbtidl> gettp,6 & copy,0,2 get ON and copy to container 2 gbtidl> gettp,7 & copy,0,3 get OFF and copy to container 3 gbtidl> subtract,2,3 (ON-OFF) (container math) gbtidl> divide,0,3 (ON-OFF)/OFF gbitidl> scale,17.34 (multiply by Tsys to give Ta=Tsys*(ON-OFF)/OFF) gbtidl>!g.s[0].units='ta (changing meta data units from counts to Ta [K]) gbtidl> setregion (select regions for baseline removal) gbtidl> nfit,3 (use 3 rd order polynominal for baseline fitting) gbtidl> bshape (fit baseline) gbtidl> baseline (remove baseline) gbtidl> gsmooth,3,/decimate (Gaussian smooth with width of 3 channels) gbtidl> fitgauss (fit Gaussian to data) gbtidl> keep (save current data in container 0 to output file!g.s[0].units='ta')

20 Frequency Switching Example: DEMO_frequency_switching GBTIDL -> offline, TGBT17A_506_11 GBTIDL -> summary (give summary of session) GBTIDL -> getfs,10 (reduce frequency switched data) GBTIDL -> gettp,10,sig=1 (look at one freq) GBTIDL -> freeze GBTIDL -> gettp,10,sig=0 (look at other freq) GBTIDL -> oshow Change between MHz and Channels at top of IDL plotting window to show how this works

21 GBTIDL position-switch Demo: DEMO_sdfits_HIsigref filein, sdfits_example (from DATAdemo directory) summary gettp,56 (look at passband) getsigref,56,57 (look at one ON-OFF pair) dotri,56,70 (reduces ON-OFF-ON sequence and co-adds data for scans 56-70) Smooth data and baseline removal

22 Example script: dotri.pro pro dotri,sc1,sc2 ;;16A054 HI project ;;does ON-OFF-ON reduction for scans sc1-->sc2 ;;Session 1: sc1=16, sc2=39 sclear for ii=sc1,sc2,3 do begin print,'combining ON-OFF',ii,ii+1 getsigref,ii,ii+1,plnum=0 accum getsigref,ii,ii+1,plnum=1 accum print,'combining ON-OFF',ii+2,ii+1 getsigref,ii+2,ii+1,plnum=0 accum getsigref,ii+2,ii+1,plnum=1 accum endfor ave copy,0,10 return end

23 Argus Mapping Demo: DEMO_argus_mapping Raw data (40min observations, 167k spectra) first calibrated and reduced at about 0.2 sec per spectrum which takes ~9hrs) using argus_mapcal.pro è save15a901_27.fits filein, save15a901_27.fits (from DATAdemo directory) getrec,50000 for i=70000,70200 do begin & getrec,i & accum & end ave (13CO near channel 6000) Run gbtgridder $gbtgridder c 5900:6100 a 7 noline nocont o test3 save15a901_27.fits o Channels 5900:6100 o Averaging over 7 channels o Avoid having software do continuum subtraction (already done) $casaviewer (or ds9) to view output cube (test3_cube.fits)

24 L-band Pipeline Demo: DEMO_NGC6946_HI_pipeline Gbtidl> offline, TGBT17A_506_11 Gbtidl> summary (map scans and reference scan is 27 want on HI which is IFNUM=0) $gbtpipeline i /home/sdfits/tgbt17a_506_11/tgbt17a_506_11.raw. vegas m 14:26 refscan 27 w 0 c 1700:2300 -a 50 o Firsts calibrates the data then grids the data o Map-scans are 14:26 o Reference scan is 27 o IFNUM= 0 (spectral window = 0) o Channels 1700:2300 o Average 50 channels $casaviewer (or ds9) to view output cube data

25 Argus deep frequency switching coadd: DEMO_argus_frequency_switching_deep_coadd GBTIDL -> offline, TGBT17A_506_06 GBTIDL -> vanecal,53 (derive atmospheric parameters and Tsys* for all beams) GBTIDL -> argus_fsw,55,53,ifnum=0,fdnum=9 (calibrate one scan for center beam) GBTIDL -> for i=55,86 do begin & argus_fsw,i,53,ifnum=0,fdnum=9 & accum &end GBTIDL -> ave (Coadd all scans for one beam) GBTIDL -> argus_fsw_coadd,55,86,53,ifnum=0 (coadd all scans for all beams [takes 20min])

26 Saving data and Mapping fileout, mysave.fits Reduce data like you want then type: keep After calibration within gbtidl can run gbtgridder (eg.): gbtgridder c 11000:11251 a 7 --noline nocont o myout mysave.fits èmyout_cube.fits myout_weight.fits

27 Running the Pipeline Works for receivers with noise diodes (designed orignally for KFPA): %gbtpipeline i my.sdfits.raw.vegas m 14:24 refscan 13,26 (where are the map scans and 13 and 26 are the reference scans) èwill calibrate and do the gridding

28 Example of reducing W-band DCR Data (daisy scan of point source) Ø sdfits -backends=dcrtrco_ scans=1 IDL>ftab_ext,INdcr,[7,13,15,19,59,60],data,ra,dec,scan,pl num,fdnum,exten_no=1 {calibrate data based on plnum and fdnum: data1=gain*data} IDL> hpfilt,data1,100,10,ndata IDL>mymap=griddata(ra,dec,ndata,dimension=[60,60]) IDL>smmap=filter_image(mymap,FWHM_gaussian=3) IDL> atv,smmap